Tuesday, April 16, 2013

On the Ex-Ante and the Ex-Post

Some thoughts on the occasion of receiving an email from a friend. He went down to the Boston marathon to watch his friend finish, and was planning to view things at the finish line. He found it too crowded, and walked up the street. This caused him to miss the first explosion, which was right near where he was originally standing. It also put him right next to where the second explosion was. By sheer coincidence, in the shock from the first blast, he started to walk towards the finish line, the site of the initial explosion. This caused him to be just far enough away from the second bomb when it exploded, right near where he'd been. He managed to escape unhurt.

I don't know about you, but studying enough statistics has had a subtle but deep effect on how I view the world. We who aspire to rationality make all our decisions in the realm of ex-ante calculations. When you understand probability, you realize that it doesn't make any sense to regret betting on heads when tails comes up as the winner, just as it doesn't make any sense to thrill at having chosen tails. You can only organise your life around things you know now, and decisions are only truly good or bad when evaluated according to what you knew at the time.

And yet...

When all that's said and done, you don't eat the expectation, you eat the coin flip. Every day, it tumbles through the sky, and all you can do is gird your loins and brace for whatever happens at the end. You plan and plan, and still, one day when you're not thinking, everything comes down to whether or not you took three steps in the right direction or not.

Different people give lots of different names to that - chance, luck, fate, God, Kamma. Ultimately, they're describing the same thing - whether you live to write the email or you don't.

In the end, it just wasn't your day to die. I'm extraordinarily glad of that. You get to see the sunrise and keep your health, and we get to keep our friend. Somewhere else, other people are receiving much sadder emails.

Such is life.

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